1. Field of the Invention
The present invention relates to a wireless resource allocation apparatus and a corresponding method.
Priority is claimed on Japanese Patent Application No. 2009-214854, filed Sep. 16, 2009, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In recent years, LTE (long term evolution), one of 3GPP (third generation partnership project) standards, is known as an advanced mobile communication method for implementing high-speed and wide-range wireless transmission (see, for example, Non-Patent Document 1: 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation”).
In the LTE standard, an OFDMA (orthogonal frequency division multiple access) method is used as a wireless transmission method for downstream links (i.e., links from a base station to terminal stations). The OFDMA method is a multi-carrier transmission method which performs communication using a wide-band signal which is formed by sub-carriers whose frequencies are orthogonal to each other. In this method, each user (terminal station or terminal unit) uses an individual sub-carrier, so that a multi-access connection between a single base station and a plurality of users can be realized.
Also in the LTE standard, a mechanism called “semi-persistent scheduling” for efficiently transmitting a VoIP (voice over Internet protocol) traffic is defined in a standard specification. The semi-persistent scheduling effectively uses characteristics of packets in a VoIP traffic which arrive regularly, and the scheduling is performed by the following procedure.
(1) A base station informs each terminal station in advance of setting information such as packet transmission period based on a semi-persistent scheduling (i.e., “semi-persistent scheduling packet transmission period”) by means of an RRC (radio resource control) layer signaling.(2) The base station informs each terminal station of a sub-frame and a resource block (RB) which are first used in the semi-persistent scheduling by means of a control signal through a physical layer (PHY layer).(3) After that, the base station sends no control signal through the physical layer, and sends each packet of the VoIP traffic to each terminal station, by using the transmission period, the sub-frame, and the resource block in the relevant sub-frame, which have been designated in the above steps (1) and (2).
The advantage of the above procedure is to have the above step (3) in which the base station does not need to send the control signal through the physical layer, so that no control channel in the physical layer is subjected to pressure and many VoIP traffics can be contained in the control channel.
As described above, in the semi-persistent scheduling defined in LTE, the semi-persistent scheduling packet transmission period, and the sub-frame and resource block for transmission are determined in advance, and each terminal station receives packets of a VoiP traffic sent from the base station. Here, for the usage of the relevant wireless resource, there is a tacit agreement between the base station and each terminal station.
However, in actual VoIP traffics, especially in downstream links, each packet may not arrive at a scheduled time, due to, for example, congestion in an upper-layer network. Additionally, in a VoIP traffic (e.g., AMR (adaptive multiple-rate)) which employs a variable bandwidth codec, the actual operation may differ from an assumption defined when reserving a wireless resource based on the semi-persistent scheduling. For example, packets of a VoIP traffic having a size out of the relevant assumption may arrive. In such a case, it is impossible to perform efficient wireless resource allocation.